1. Field of the Invention
The present invention relates to a structure of housing a battery etc. More particularly, it relates to a structure of housing a battery etc. in an instrument (for example, a remote keyless entry system transmitter or the like) which requires a reliable waterproofing performance, and needs an operation of replacing a built-in battery.
2. Description of Related Art
A remote keyless entry system is a convenient system with which it is possible to carry out a locking/unlocking of a door and the like, without using a mechanical key, simply by operating a push button of a transmitter contained in as small a casing as a matchbox. Also, as a progressive type of this, there is also a system which has eliminated a need to operate the push button of the transmitter. In the progressive type system, it is possible to carry out a locking/unlocking of a vehicle door by pressing an entry button while wearing the transmitter, and it is not necessary to take the transmitter out of a pocket each time.
As such transmitters are all used outdoors, waterproofing measures against wet weather and the like are indispensable. Also, as all of them operate with a disposable battery, an easiness of the operation of replacing the battery must also be considered.
<First Related Art>
FIG. 7 is a view showing a first related art (refer to, for example, JP-A-11-81762 ([0038] to [0039], FIG. 3) (Patent Document 1)). In the figure, a transmitter 100 has: a main body 101, as small as a matchbox, configured of upper and lower halved casings 101a and 101b; a battery 102 which is housed in a battery housing portion 101d inside the main body 101 via a battery housing hole 101c opened in a bottom surface of one casing 101a; a waterproof O-ring 103 attached to a peripheral edge of the battery housing hole 101c; and a circular lid 104 which closes the battery housing hole 101c in a condition in which the O-ring 103 is nipped. Various kinds of push button such as, for example, a locking button and an unlocking button, are provided on a surface (a surface which is hidden out of sight at the back) of the other casing 101b. 
An advantage of the first related art lies in that an operation of replacing the battery 102 is easy. That is, it lies in that, by fitting a coin or the like at hand in a groove 104a of the circular lid 104 and turning it, it being possible to easily remove the circular lid 104, it is possible to replace the battery 102 without requiring a special tool.
Meanwhile, in the first related art, there is the following disadvantage. Firstly, as there is less empty space on a surface of the main body 101, a range being narrow to which can be attached, for example, a maker emblem, a radiowave authentication seal or the like, there is no design freedom. That is, as the battery housing hole 101c and the circular lid 104 exist on a surface of the casing 101a, and furthermore, the various kinds of push button exist on the surface of the casing 10b, there is a disadvantage that the maker emblem, the radiowave authentication seal or the like can be attached only to a very narrow range avoiding them. Also, although one of waterproof places of the transmitter 100 is between the battery housing hole 101c and circular lid 104 of the casing 101a, there is also a disadvantage that, in the event that an attachment error of the O-ring 103, or a failure to attach it, occurs during the operation of replacing the battery 102, rain water enters therefrom, causing damage to the electronic substrate inside the main body 101.
<Second Related Art>
FIG. 8 is a view showing a second related art (refer to, for example, JP-A-2003-201781 ([0042], FIG. 2) (Patent Document 2), JP-A-2003-90152 ([0077], FIG. 2) (Patent Document 3) and JP-A-2001-339176 ([0012] to [0015], FIG. 2) (Patent Document 4)). In the second related art too, in the same way as in the heretofore described first related art, a transmitter 105 has a main body 106, as small as a matchbox, configured of upper and lower halved casings 106a and 106b, but a “circular lid for battery replacement” such as the one of the heretofore described related art does not exist. It is arranged in such a way as to replace a battery 107 by disassembling the upper and lower halved casings 106a and 106b each time it is necessary. This kind of battery replacement method is referred to as a “casing disassembly method”.
A spring terminal 106c abutting against one electrode of the battery 107, a conductive sheet 106d making electrical connection with the spring terminal 106c, and a waterproof seal 106e on a peripheral edge of an opening of the casing 106a are attached to an inner surface of one casing 106a, and also, a spring terminal 106f abutting against the other electrode of the battery 107, an electronic substrate 108 mounted with a prescribed electronic circuit which operates with a terminal voltage of the battery 107 supplied via these two spring terminals 106c and 106f as a power source, and a holding body 106g which holds and positions a periphery of the battery 107, are attached to an inner surface of the other casing 106b. 
The second related art has a number of advantages as follows. That is, as no circular lid for battery replacement exists, sufficient empty space on a surface of the main body 106 is secured. Consequently, there is an advantage that a degree of freedom of attachment of the maker emblem, the radiowave authentication seal or the like is high. In addition, there is an advantage that, by causing the upper and lower halved casings 106a and 106b to have an elastic fit (a snap connection), it is possible to easily disassemble the main body 106 using, for example, a coin or, as the case may be, a fingernail, without requiring a special tool, and easily carry out the replacement of the battery 107. Moreover, as a waterproof place is limited to only one place (the waterproof seal 106e) between the upper and lower halved casings 106a and 106b, there is an advantage that, by adhesively fixing the waterproof seal 106e, it is possible to avoid a peeling off or the like of the waterproof seal 106e during the operation of replacing the battery 107. From these advantages, many of today's remote keyless entry system transmitters employ this casing disassembly method.
Meanwhile, in the heretofore described second related art (the casing disassembly method one), although there are excellent advantages in that the degree of freedom of replacement of the maker emblem, the radiowave authentication seal or the like is high, the battery replacement is easy, and a waterproofing performance can be maintained, due to the method of replacing the battery 107 by disassembling the upper and lower halved casings 106a and 106b, it has happened that a dropping off of the electronic substrate 108 is caused during the replacement operation. In order to avoid this, for example, as shown in FIG. 8, a measure to fix the electronic substrate 108 to the casing 106b with a screw 109 is taken in some cases, but this kind of screwing measure is not preferable because it involves a complication of a manufacturing process.
<Third Related Art>
In response to this disadvantage, Patent Document 4 proposes the following improved structure (a third related art).
FIG. 9 is a sectional view of a main portion at a transmitter assembly time, showing the third related art (a view of a main portion extracted from FIG. 2 in Patent Document 4). In the figure, first of all, an elastic piece 111a of an inner casing 111 is engaged with a peripheral edge of an electronic substrate 110 and, in the engaged condition, the electronic substrate 110 and the inner casing 111 are fitted into a sealing rubber 112. After that, the assembled body (the electronic substrate 110+the inner casing 111+the sealing rubber 112) are pushed into an outer casing 113, engaging a projection 112a (a pressure deformed portion caused by a convex portion 111b of the inner casing 111) of the sealing rubber 112 with a depression 113a in an inner peripheral side surface of the outer casing 113. By assembling in this way, eventually, the outer casing 113, the sealing rubber 112, the inner casing 111 and the electronic substrate 110 are integrated, and it does not happen that the electronic substrate 110 drops off during the battery replacement.
However, in the third related art, although it is possible to avoid the dropping off of the electronic substrate 110 during the battery replacement, the following problem can be considered. That is, when fitting the electronic substrate 110 and the inner casing 111 into the sealing rubber 112, as a strong friction occurs between the projection 112a of the sealing rubber 112 and a projection 113b of the outer casing 113, in some cases, there is a possibility of involving damage, such as a breakage, to a portion of the sealing rubber 112 subjected to the friction.
<Fourth Related Art>
As a related art which has eliminated this kind of disadvantage, the following one (a fourth related art) is known.
FIGS. 10A and 10B are views showing the fourth related art (refer to, for example, JP-A-2005-159221 ([0028] to [0031], FIG. 1) (Patent Document 5). A transmitter in the fourth related art includes an upper casing 114 having a box shape with a bottom, a sealing rubber 115 which covers an inner surface of the upper casing 114, an electronic substrate 116 fitted inside the sealing rubber 115, and an inner plate 117 which prevents a dropping off of the electronic substrate 116.
The inner plate 117, being an integrally molded article having a center bending type undivided dual-partitioning structure, is molded to include, at least, projections 117a and 117b which are engaged with grooves 114a and 114b formed in the inner surface of the upper surface 114, and elastic pieces 117c and 117d which are engaged with notches 116a and 116b formed in a peripheral edge of the electronic substrate 116. Furthermore, the inner plate 117 is placed on the electronic substrate 116 in a bent condition (the condition in FIG. 10A), and it is arranged in such a way that, by applying a force such as to eliminate the bent condition (refer to the outline arrow in FIG. 10A) to the inner plate 117, as well as the projections 117a and 117b of the inner plate 117 being engaged with the grooves 114a and 114b of the upper casing 114, the elastic pieces 117c and 117d of the inner plate 117 are engaged with the notches 116a and 116b of the electronic substrate 116.
In the fourth related art, the inner plate 117 is put into the bent condition and placed on the electronic substrate 116 and, simply by carrying out the operation of applying a force such as to eliminate the bent condition, it is possible to integrate the upper casing 114, the sealing rubber 115 and the electronic substrate 116. Then, as no unnecessary friction occurs between the sealing rubber 115 and the upper casing 114 at a time of the integration, it is possible to resolve the disadvantage of the heretofore described third related art, that is, damage to (a breakage or the like of) the sealing rubber 115.
However, in the heretofore described fourth related art, there is room for improvement for the following reason.
In the fourth related art, in the inner plate 117 after having the bent condition eliminated, although it maintains a straightened condition in an approximately flush aspect along the electronic substrate 116, the maintenance of the straightened condition is carried out exclusively by the engagement between the elastic pieces 117c and 117d formed on the inner plate 117 and the notches 116a and 116b of the electronic substrate 116. These elastic pieces 117c and 117d are components indispensable and essential to the fourth related art. This fact can be easily understood by imagining a case in which there is no elastic piece 117c or 117d. This is because, even in the event that the bent condition has been eliminated by applying the force to the inner plate 117, when the force is removed, the inner plate 117 is restored to the original condition (the bent condition) by its own restoring force.
In this way, although the elastic pieces 117c and 117d formed on the inner plate 117 are items essential to the fourth related art, there is room for improvement in that an existence of the elastic pieces 117c and 117d causes a decrease in a mounting area of the electronic substrate 116.
FIG. 11 is a view showing a problem of the fourth related art. That is, as the elastic pieces 117c and 117d of the inner plate, as shown in the figure, are arranged in such a way as to be fit in the notches 116a and 116b formed in either side surface of the electronic substrate 116, the mounting area of the electronic substrate 116 decreases by an amount of a formation area of the notches 116a and 116b. The decrease in the mounting area may be extremely small. However, as a portable transmitter, particularly the remote keyless entry system transmitter, tends to require a further miniaturization, even the extremely small decrease in the mounting area cannot be overlooked.